Solar-thermal installations comprise at least one solar collector and a water storage means, in which for example service water to be heated is stored. The solar collector is connected to a heat exchanger arranged in or on the water storage, via a heating circuit, in which a circulation pump delivering the heating medium heated by the solar collector into the heat exchanger of the water storage means and back out of this into the solar collector is arranged. It is known to control this circulation pump with regard to its speed, in dependence on the heat demand in the water storage means and on the heat quantity provided in the solar collector. For this, the known installations comprise at least two temperature sensors, one on the solar collector and one in the water storage means. These two temperature sensors are to be connected to a control device which as the case may be, can be integrated into the circulation pump. Such connections of the sensors are prone to error with regard to assembly and in operation.